The procoagulants, thromboplastin (tissue Factor) and platelet factor 3 are lipoproteins. Their protein moieties act biologically and biochemically as phospholipid dependent enzymes. The purpose of this project is to isolate, characterize, and compare the proteins involved in expression of procoagulant activity. The proteins from brain and lung thromboplastins have been isolated, partially purified, and characterized. Further purification is required prior to completion of definitive structural, immunologic, and phospholipid dependence studies. This process is ongoing, as is isolation and purification of PF 3 proteins. Purification without biologic denaturation has been the primary difficulty encountered. Procoagulant potential is required to ascertain which of the several proteins isolated is responsible for activity when recombined with the appropriate phospholipid. After purification, synthesis sites and cellular localizaion studies can be conducted. The brain-protein-phospholipid requirements are currently being evaluated employing liposomes composed of synthetic phospholipids. Human platelet antiheparin, platelet factor 4 (PF 4) isolated by affinity chromatography on heparin-Sepharose has been characterized including its primary structure. Its heparin binding peptides are being isolated and characterized. Partial sequence of the bovine product has been achieved with completion envisioned within the year. Its heparin binding will also be characterized via peptide isolation and affinity chromatography. The ultimate goal of the above studies on platelet and tissue procoagulants is to define the substances and mechanisms of thrombosis initiation. Studies on PF 4 are being conducted to develop a non-toxic synthetic antiheparin for clinical use.